Tinytags Monitor Bat Swarming Sites in Kent

Temperature and relative humidity data loggers are used to monitor bat swarming sites including Dover Castle.

Seasonal temperature and relative humidity changes are being recorded as part of research into bat swarming behaviour.

Bat lovers in the Dover area are very lucky to have an abundance
of underground workings, and volunteers from the Kent Bat Group
monitor as many of these as possible - particularly in winter as
part of the Bat Conservation Trust's National Bat Monitoring
Programme hibernation counts.

Recently, the Group has begun to realise the importance of some
of these as autumn bat swarming sites. This activity seems to be
about mating but also might have a social function, as young
non-breeding bats are often found in the swarms: 'bat festivals'
perhaps!

For four years now the Group has been monitoring autumn swarming
bats at a Palmerston fort built when the fear of a Napoleonic
invasion was at its height. Last year a ringed Natterer's bat, most
likely one from the fort, was seen flying in a well in Dover
Castle, within a kilometre to the south. It is possible that the
same bats were visiting both sites: it is often considered that
bats are faithful to one swarming site, but this may not always be
the case.

Having obtained the appropriate licences from Natural England,
members of the Group set about ringing as many bats as they could
catch in the swarming area and monitoring their activity. Gemini
supplied two Plus 2
TGP-4500 data loggers to monitor temperature and relative
humidity at the castle. Recording this information is important
because bat swarming behaviour is not well understood and it is
vital to have some idea of the environmental conditions that may
trigger or delay swarming. These robust, waterproof data loggers
are ideally suited to the environmental conditions in the
underground area of the castle, and can be left for long periods if
required to minimise the impact of human intrusion on the site.

Similar monitoring has been carried out at the nearby fort for
some time. The data is still being analysed but suggests that
swarming takes place during the same time frame each year, but the
focus of activity sometimes varies within the fort, possibly
depending on meteorological conditions.

Temporary light tags were placed on a few Natterer's bats, in
the hope it would help determine their destination. It was intended
to analyse all the data and manual observations from both sites,
however the week planned for this operation was one of the windiest
of the season and this was not as successful as hoped, as the bat
numbers were lower than expected. The Group hopes for better
results in future years, but is now certain that the autumn
swarming activity in the area is significant; yet more research is
needed, through monitoring of these sites, for several more
autumns.